The commercial production of wrought copper base alloys is seriously affected by edge cracking of the alloys during hot rolling or working. Silicon-tin bronzes in particular are susceptible to the edge cracking phenomenon because of the tendency of the silicon and tin elements to segregate in the alloy during casting. Ternary alloys which contain silicon and tin are even more susceptible to the edge cracking phenomenon, but these ternary alloys are nonetheless desirable for commercial production because they provide a good combination of stress corrosion resistance, high strength and formability.
Various means have been employed to counteract the edge cracking phenomenon of such alloys. Such means have included both different combinations of elemental additions and ways to vary the hot working process. For example, copper alloys which contain impurities such as lead and bismuth, as outlined in "A Preliminary Assessment of the Value of Minor Alloy Additions in Counteracting the Harmful Effect of Impurities on the Hot Workability of Some Copper Alloys" by R. J. Jackson et al. in the Journal of the Institute of Metals, Volume 98 (1970), Pages 193 through 198, may have their tendencies to crack during hot working reduced by the addition of such materials as thorium, uranium and mischmetal. These copper base alloys include admiralty brass, nickel silver, cupro nickel and 95/5 phosphor bronze. Ductility increases (or increases in hot workability) have also been noted for a mischmetal-phosphorus copper base alloy in "Effect of Misch Metal on Mechanical Properties of Some Industrial Copper Based Alloys" by U. K. Duysemaliyev in the Transactions of the Institute of Metallurgy and Beneficiation of the Academy of Sciences of The Kazakh SSR, Metallography and Pressure Working of Metals, Volume 10, No. 3 (1964), Pages 55 through 58. In this particular article, it has been discovered that mischmetal in amounts of approximately 0.05 to 0.5%, when added to copper-zinc alloys, increases the ductility of such alloys. In neither of these articles is the addition of such materials as mischmetal to silicon-tin copper base alloys disclosed.
Another method of counteracting stress corrosion failure in copper base alloys is indicated in U.S. Patent No. 3,923,555, which is assigned to the same Assignee as the present invention. This patent in particular describes a copper base alloy which consists essentially of from 1 to 4.5% silicon, from 1 to 5% tin, balance copper wherein the total silicon plus tin content is at least 3.5%. This particular alloy system provides copper base alloys which have high mechanical strength, excellent stress corrosion resistance and also good general corrosion resistance. These particular alloys are quite useful for purposes which require good formability in the particular alloys being worked.
It is therefore a primary object of the present invention to provide a copper base alloy which is resistant to edge cracking during hot working.
It is an additional object of the present invention to provide an alloy as above which reduces said edge cracking through an elemental addition to the alloy, rather than a particular method of hot working.
It is a further object of the present invention to provide an alloy as above which utilizes an elemental addition which is readily available.
Further objects and advantages of the present invention will become more apparent from a consideration of the following specification.